/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.metrics.groups;

import org.apache.flink.annotation.Internal;
import org.apache.flink.runtime.metrics.MetricRegistry;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Abstract {@link org.apache.flink.metrics.MetricGroup} for system components (e.g.,
 * TaskManager, Job, Task, Operator).
 *
 * <p>Usually, the scope of metrics is simply the hierarchy of the containing groups. For example
 * the Metric {@code "MyMetric"} in group {@code "B"} nested in group {@code "A"} would have a
 * fully scoped name of {@code "A.B.MyMetric"}, with {@code "A.B"} being the Metric's scope.
 *
 * <p>Component groups, however, have configurable scopes. This allow users to include or exclude
 * certain identifiers from the scope. The scope for metrics belonging to the "Task"
 * group could for example include the task attempt number (more fine grained identification), or
 * exclude it (for continuity of the namespace across failure and recovery).
 *
 * @param <P> The type of the parent MetricGroup.
 */
@Internal
public abstract class ComponentMetricGroup<P extends AbstractMetricGroup<?>> extends AbstractMetricGroup<P> {

    /**
     * Creates a new ComponentMetricGroup.
     *
     * @param registry     registry to register new metrics with
     * @param scope        the scope of the group
     */
    public ComponentMetricGroup(MetricRegistry registry, String[] scope, P parent) {
        super(registry, scope, parent);
    }

    @Override
    public Map<String, String> getAllVariables() {
        if (variables == null) { // avoid synchronization for common case
            synchronized (this) {
                if (variables == null) {
                    variables = new ConcurrentHashMap<>();
                    putVariables(variables);
                    if (parent != null) { // not true for Job-/TaskManagerMetricGroup
                        variables.putAll(parent.getAllVariables());
                    }
                }
            }
        }
        return variables;
    }

    /**
     * Enters all variables specific to this ComponentMetricGroup and their associated values into the map.
     *
     * @param variables map to enter variables and their values into
     */
    @Override
    protected abstract void putVariables(Map<String, String> variables);

    /**
     * Closes the component group by removing and closing all metrics and subgroups
     * (inherited from {@link AbstractMetricGroup}), plus closing and removing all dedicated
     * component subgroups.
     */
    @Override
    public void close() {
        synchronized (this) {
            if (!isClosed()) {
                // remove all metrics and generic subgroups
                super.close();

                // remove and close all subcomponent metrics
                for (ComponentMetricGroup group : subComponents()) {
                    group.close();
                }
            }
        }
    }

    // ------------------------------------------------------------------------
    //  Component Metric Group Specifics
    // ------------------------------------------------------------------------

    /**
     * Gets all component metric groups that are contained in this component metric group.
     *
     * @return All component metric groups that are contained in this component metric group.
     */
    protected abstract Iterable<? extends ComponentMetricGroup> subComponents();
}
